Nakatsu is a castle town centered around Nakatsu Castle, which is open to visitors. The modernised interior comprises a museum with samurai armor, old maps and information about Rangaku (Dutch studies), for which Nakatsu was an important center in the Edo era. There are views from the top of the castle keep.
Visitors can see the residence of the most celebrated member of the Okudaira clan of Nakatsu, Fukuzawa Yukichi, and the memorial hall there. It is close to the castle and a 15-minute walk from the station.
Nakatsu is in the northwest corner of Ōita Prefecture, Kyushu. To the east of Nakatsu is Usa and to the southwest is Hita. Nakatsu touches the border of Fukuoka Prefecture on its west. To the northeast is the Suohnada Sea. The city covers an area of 491.09 square kilometers, 80% of which is mountainous. There is a wide stretch of flat, agricultural land which begins at the mouth of Yamakuni River and extends to Mt. Hiko.